SUPERCONDUCTING ELECTRICAL MACHINE WITH TWO PART ROTOR WITH CENTER SHAFT CAPABLE OF HANDLING BENDING LOADS
A superconducting electrical machine includes a rotor and a stator. The stator defines a cavity. The rotor is configured to rotate about a longitudinal axis. The rotor is disposed at least partially within the cavity. The rotor includes a shaft configured to rotate with the rotor, a rotor active section including at least a rotor torque tube and a superconductor, and a first re-entrant end attaching the shaft to the rotor active section. At most a threshold fraction of a bending force applied to the shaft is communicated to the rotor active section.
The present invention relates generally to the field of electrical machines for energy conversion, such as motors and generators. Motors convert electricity into mechanical energy. Generators generate electricity by converting mechanical energy into electrical energy. A prime mover, such as an engine driving a rotating shaft, provides the mechanical energy. A rotor having permanent magnets or electromagnets rotates with the rotating shaft, generating a magnetic field that causes electricity to be generated in a stationary stator.
Superconducting electrical machines, such as a superconducting generator, use the principle of superconductivity to significantly reduce the electrical resistance in the conductors of the generator. Superconductivity requires maintaining the conductors at very low temperatures. Forces received from the prime mover can cause structural damages to a superconducting electrical machine, and the damages may be exacerbated by the very low temperatures.
SUMMARY OF THE INVENTIONOne embodiment of the invention relates to a rotor. The rotor is configured to rotate about a longitudinal axis. The rotor includes a shaft disposed along the longitudinal axis. The rotor also includes a first re-entrant end attaching the shaft to a rotor active section. At most a threshold fraction of a bending load applied to the shaft is communicated to the rotor active section.
Another embodiment relates to a superconducting electrical machine. The superconducting electrical machine includes a stator disposed coannular with a longitudinal axis. The stator defines a cavity. The superconducting electrical machine also includes a rotor configured to rotate about the longitudinal axis. The rotor is disposed at least partially within the cavity. The rotor includes a shaft configured to rotate with the rotor, a rotor active section including at least a rotor torque tube and a superconductor, and a first re-entrant end attaching the shaft to the rotor active section. At most a threshold fraction of a bending load applied to the shaft is communicated to the rotor active section.
Another embodiment relates to a system for generating electricity. The system includes a prime mover configured to rotate a shaft about a longitudinal axis. The system also includes a superconducting electrical machine, including a stator disposed coannular with the longitudinal axis, and a rotor configured to rotate about the longitudinal axis. The rotor includes a shaft disposed along the longitudinal axis and a rotor active section surrounding and coannular with the rotor torque tube, wherein a first re-entrant end attaches the shaft to the rotor active section. At most a threshold fraction of a bending load applied to the shaft by the prime mover is communicated to the rotor active section.
Alternative embodiments relate to other features and combinations of features as may generally be recited in the claims.
The invention will become more fully understood from the following detailed description, taken in conjunction with the accompanying figures, in which like reference numerals refer to like elements.
Before turning to the figures, which illustrate the exemplary embodiments in detail, it should be understood that the present application is not limited to the details or methodology set forth in the description or illustrated in the figures. It should also be understood that the terminology is for the purpose of description only and should not be regarded as limiting.
Referring generally to the figures, superconducting electrical machines include a stator supported in a stator frame and a rotor configured to rotate in a cavity defined by the stator. The rotor and stator are each surrounded by a cryostat to maintain a vacuum at superconducting temperatures around the rotor and the stator. A cryocooler provides coolants to the rotor and the stator to maintain the rotor and the stator at superconducting temperatures. The rotor may be rotated using mechanical energy from a prime mover (e.g., engine, gas turbine, wind turbine, etc.), or may use electricity to drive a load. The rotor and stator each include active sections in which superconductive processes may take place, in which superconducting temperatures may be achieved, and/or which are involved in the electromagnetic behavior of the superconducting electrical machine. The rotor is configured to rotate about a longitudinal axis. A shaft, which may be received from the prime mover, rotates the rotor. The rotor includes re-entrant ends attaching the shaft to an active section of the rotor, such as a rotor torque tube. The re-entrant ends provide high thermal resistance pathways to help maintain the superconducting temperatures. The re-entrant ends need to be flexible to avoid high thermal stresses. The re-entrant ends are separately attached to the active section, which may undergo thermal contraction, and each re-entrant end is carried by its own bearing. The strong, stiff center shaft helps the superconducting electrical machine to carry bending loads, while providing a secure mounting for outboard ends of the re-entrant ends. The center shaft may remain at or close to ambient temperature, such that it undergoes minimal thermal contraction, allowing for easier bearing placement and the use of alloys that could otherwise be negatively affected by low temperatures. A bending load applied to the shaft is communicated to the superconducting electrical machine active section by at most a threshold fraction of the bending load.
Referring to
Superconducting electrical machine 100 may include a pair of bracket assemblies 108, 108′ disposed at a drive end 112 and a non-drive end 116 of the superconducting electrical machine 100. The pair of bracket assemblies 108, 108′ may include a pair of bearings to support a rotor and accommodate rotation of the rotor about a longitudinal axis 10 (see, e.g., rotor 150 shown in
A drive end 112 is an end region of a superconducting electrical machine 100 proximate to a prime mover, such as a wind turbine, and at which a shaft (e.g. shaft 152 shown in
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In various embodiments, a superconducting electrical machine 100 is driven by various prime movers. For example, the superconducting electrical machine 100 may be driven by an engine, such as an engine using oil, gasoline, diesel, or other fossil fuels as a fuel source. The superconducting electrical machine 100 may be driven by a gas turbine. The superconducting electrical machine 100 may be driven by a nuclear reactor steam turbine, such as in a naval submarine. The superconducting electrical machine 100 may be used in various naval contexts, such as with oil, gasoline, or diesel engines; with gas turbines; in coordination with a propulsion motor benefiting from the high specific torque of the superconducting electrical machine 100; etc.
In some embodiments, a wind turbine 128 includes a plurality of blades 132 configured to rotate a shaft 152 when acted upon by a force, such as a force generated by wind. The plurality of blades 132 may extend radially from a central hub 130 which is coupled to the shaft 152, and the plurality of blades 132 may rotate the central hub 130 and in turn rotate the shaft 152 when acted upon by a force. The plurality of blades 132 may include three blades 132 arranged in a circular configuration. In some embodiments, the plurality of blades 132 are arranged in a circular configuration and spaced equidistantly from each other, the plurality of blades being spaced by approximately 60 degrees from each other.
In some embodiments, a bending load is transmitted from a prime mover, such as wind turbine 128, to a shaft 152 which rotates a rotor 150 of a superconducting electrical machine 100. A bending load may be any load applied to the shaft 152 not involved in the rotation of the shaft 152 about the longitudinal axis 10 to rotate the rotor 150 and drive the superconducting electrical machine 100. For example, a bending load may be a load applied in a direction not parallel to the longitudinal axis 10. A bending load may lead to a bending moment which may lead to the shaft 152 no longer being parallel to the longitudinal axis 10, or which may lead to the shaft 152 rotating in a plane containing the longitudinal axis 10. A bending load may be induced by action of the wind turbine 128 on the shaft 152; a bending load may be induced by forces remote from the wind turbine 128 acting on the wind turbine 128, which are then transmitted to the shaft 152.
In some embodiments, a shaft 152 may pass directly through and be supported by a bracket and a bearing at the drive end 112 of the superconducting electrical machine 100, into a rotor 150. The shaft may at least partially coincide with a longitudinal axis 10. The shaft 152 may be coupled to the rotor 150 to directly rotate the rotor 150 and drive the superconducting electrical machine 100. The shaft 152 may be attached to a rotor active section via re-entrant ends (see, e.g., rotor active section 154 shown in
In some embodiments, the shaft 152 acts as a strong, stiff center in the superconducting electrical machine 100 to carry bending loads. The shaft 152 may provide a secure mounting for re-entrant ends 172, 174. In some embodiments, the shaft 152 remains relatively close to ambient temperature, such that the shaft 152 undergoes low amounts of thermal contraction. As such, the shaft 152 minimizes the need for complex bearing systems to accommodate thermal contraction in the shaft, while also allowing for the use of alloy materials in the superconducting electrical machine 100 that would otherwise be negatively impacted by low temperatures.
The shaft 152 may transfer a torque to an active section of the rotor 150 (e.g., rotor active section 154 shown in
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In some embodiments, the bending load may be transmitted from the shaft 152 to a pair of bracket assemblies disposed at the drive end 112 and the non-drive end 116 of the superconducting electrical machine 100 (e.g., bracket assemblies 108, 108′ shown in
In some embodiments, a re-entrant end (e.g., re-entrant drive end 172, etc.) includes a re-entrant length. The length may be tailored based on a balance between a stiffness for the re-entrant end and a resistance to heat transfer through the re-entrant end. The length may be tailored relative to a length of other portions of a rotor 150. For example, the length may be tailored based on factors such as a maximizing a thermal pathway in order to provide maximum thermal resistance, and maintaining active section support for various forces (e.g., maintaining flexibility for accommodating thermal expansion and/or thermal contraction). For example, the re-entrant length may be at least one third of a length of a rotor torque tube (see, e.g., rotor torque tube 200 shown on
In some embodiments, a re-entrant end (e.g., re-entrant end 172, etc.) is configured to have a first temperature at a first point and a second temperature at a second point. The first point may be a point proximate to where the re-entrant end 172 attaches to a shaft 152. The first temperature may be approximately a temperature of the shaft 152 close to a room temperature (e.g. 293 Kelvin, 298 Kelvin, etc.). The second point may be a point proximate to where the re-entrant end 172 attaches to a rotor torque tube 200. The second temperature may be approximately a superconducting temperature achieved in the rotor torque tube 200 or other components of an active section of the rotor 150 (see, e.g., rotor active section 154 shown in
In some embodiments, a rotor 150 or a portion of a rotor 150 (e.g., rotor windings 216, rotor torque tube 200, etc.) undergoes a volume change due to thermal expansion or contraction due to a change in temperature from a first temperature to a second temperature. The re-entrant end 172 may be configured to compensate for the volume change. For example, portions of a rotor 150 at superconducting temperatures may undergo thermal contraction. Ordinarily, thermal contraction may cause axial stress (e.g., stress in a direction substantially parallel to a longitudinal axis 10) on other portions of the rotor 150 or the superconducting electrical machine 100. The re-entrant end 172 may provide an extended pathway for conduction of thermal energy between a portion of the rotor 150 at a superconducting temperature and a portion of the rotor 150 (e.g. shaft 152) exposed to a room temperature. As such, a temperature gradient between the superconducting temperature and the room temperature does not cause a significant stress.
Generally, the term volume change may encompass any change in a volume of a superconducting electrical machine or a component of a superconducting electrical machine (e.g. a rotor, a stator, superconducting windings, etc.). A volume change may refer to any change in dimensions of a superconducting electrical machine or a component of a superconducting electrical machine, such as an expansion or a contraction. A volume change may be a thermal volume change induced by a change in temperature of a material. An expansion or a contraction may occur in one dimension, two dimensions, or three dimensions. An expansion or contraction may occur in some dimensions at some temperatures, and in other dimensions at other temperatures. An expansion or contraction may be measured by various techniques, such as by comparing a change in a dimension of a material (e.g. length, etc.), to an initial dimension of the material. A material property such as a thermal expansion coefficient may be used regarding volume changes for a material. The thermal expansion coefficient may correspond to various volume changes, including a contraction that occurs when the temperature of a material decreases and an expansion that occurs when the temperature of a material increases.
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The superconducting electrical machine 100 may include a stator 160. As shown in
An outer surface of the rotor 150 may be defined by a rotor cryostat 156 which maintains a vacuum environment within the rotor 150. Cryostats, such as the stator cryostat 164 and the rotor cryostat 156, improve the ability of the superconducting electrical machine 100 to maintain a superconducting environment, by providing a vacuum environment surrounding each of the stator 160 and the rotor 150. In some embodiments, an air gap remains between the stator cryostat 164 and the rotor cryostat 156 after the rotor 150 has been positioned within the cavity 20 (see, e.g., air gap 184 shown in
In some embodiments, a rotor 150 is rotatably coupled to a shaft and may be rotated by the shaft about a longitudinal axis 10 when the shaft rotates (see, e.g., shaft 152 shown in
When a superconducting electrical machine 100 is assembled and/or being operated, a stator 160 may be disposed generally surrounding and coannular with the rotor 150. The stator 160 may be supported by a stator frame 104. The stator 160 may include a stator re-entrant drive end 168 and a stator re-entrant non-drive end 170. The re-entrant ends 168, 170 may provide an extended path along which thermal conduction occurs between the stator active section 162 and an environment surrounding the superconducting electrical machine 100, which increases a resistance to thermal conduction, thus facilitating maintaining the stator active section 162 at or below a superconducting temperature.
The stator 160 may be surrounded by an electromagnetic shield which minimizes communication of electrical signals and energy across a boundary of the stator frame 104 and the superconducting electrical machine 100 (see, e.g., electromagnetic shield 190 shown in
Referring to
A cryocooler 400 may control the temperatures and flow rates of coolants provided to a superconducting electrical machine 100, in order to control a temperature of active sections (e.g., rotor active section 154 shown in
The power converter 320 may convert electrical energy generated by the superconducting electrical machine 100 to a form compatible with electrical components outside of system 300. For example, the superconducting electrical machine 100 may generate variable frequency power, which must be rectified and inverted before transmission to an electrical grid.
The excitation device 330 may provide an excitation current to the rotor 150 so that the rotor windings 208 of the rotor 150 may generate a magnetic field. In some embodiments, control system 310 controls operation of the excitation device 330 to dynamically modulate the excitation current in response to conditions including but not limited to wind conditions. In some embodiments, a change in the excitation current leads to an inductive voltage, requiring power to be supplied from the excitation device 330 to the superconducting electrical machine 100. In some embodiments, the excitation current is modulated over long time constants (e.g., several minutes) in response to conditions including but not limited to wind conditions and/or for providing variable speed operation.
The cryocooler 400 may be coupled to a superconducting electrical machine 100, and the cryocooler 400 may drive a cooling cycle, such as a reverse-Brayton cycle, in order to provide coolants to the superconducting electrical machine 100. The coolants may pass from the cryocooler 400, which has cooled the coolants to a temperature at or below a superconducting temperature, through cooling tubes in the active sections of a rotor 150 and a stator (e.g., stator 160 shown in
In some embodiments, the coolant includes gaseous helium. Cryocooler 400 may include a Turbo-Brayton cryocooler which provides a coolant of helium (e.g., helium gas having a temperature of approximately 15-20 Kelvin, etc.) at a superconducting temperature, to a rotor 150 and to a stator (e.g., stator 160 shown in
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The rotor composite 208 may be surrounded by a rotor retention layer 212. The rotor retention layer 212 may provide additional structural support to the rotor 150 during a change in temperature from a first temperature to a second temperature, and may also provide additional structural support to the rotor 150 during operation of the superconducting electrical machine 100.
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In some embodiments, a rotor 150 includes rotor windings 216 configured to superconduct at or below a superconducting temperature. A re-entrant end, such as rotor re-entrant end 172, is disposed between a shaft (e.g., shaft 152 shown in
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In some embodiments, a plurality of rotor segments 173 form multiple passes. In some embodiments, at least two of the plurality of rotor segments 173 are substantially parallel to each other, to a rotor torque tube 200, and to a longitudinal axis (e.g., longitudinal axis 10 shown in
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In some embodiments, the plurality of rotor segments 175 form multiple passes. In some embodiments, at least two of the plurality of rotor segments 175 are substantially parallel to each other, to a rotor torque tube 200, and to a longitudinal axis (e.g., longitudinal axis 10 shown in
In some embodiments, the long pathway for conduction of thermal energy provided by the re-entrant ends 172, 174 allows for standard stationary bearings to be used to support the rotor 150. The long pathway ensures that a rate of heat transfer from exterior portions of the superconducting electrical machine 100, such as a drive end 112 region of the rotor 150 or a non-drive end 116 region of the rotor 150, is sufficiently low so as to minimize the cooling load required to maintain the temperature of superconductors (e.g., rotor windings 216, etc.) at or below a superconducting temperature. The long pathway also prevents communication of low temperature conditions in a center of the rotor 150 to the drive end 112 region or the non-drive end region 116, minimizing axial stresses in a shaft (e.g., shaft 152 shown in
As shown in the figures and described in the written description, a superconducting electrical machine 100 may be fully superconducting: both a rotor 150 and a stator 160 are capable of operating in a superconducting fashion, as rotor windings 216 and stator windings 228 are each able to superconduct when maintained at a temperature no greater than a superconducting temperature. In other embodiments, a superconducting electrical machine may be partially superconducting. For example, just a rotor, or just a stator, may be configured to superconduct. In some embodiments, only one of a rotor or a stator may be provided with a composite such as rotor composite 208 or stator composite 232. In some embodiments, only one of a rotor 150 or a stator 160 may be provided with cooling tubes, such as rotor cooling tubes 220 or stator cooling tubes 224, in order to maintain respective superconductors at or below a superconducting temperature.
The construction and arrangement of the systems and methods as shown in the various exemplary embodiments are illustrative only. Although only a few embodiments have been described in detail in this disclosure, many modifications are possible (e.g., variations in size, dimensions, structures, shapes and proportions of the various elements, values of parameters, mounting arrangements, use of materials, colors, orientations, etc.). For example, the position of elements may be reversed or otherwise varied and the nature or number of discrete elements or positions may be altered or varied. Accordingly, all such modifications are intended to be included within the scope of the present disclosure. The order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments. Other substitutions, modifications, changes, and omissions may be made in the design, operating conditions and arrangement of the exemplary embodiments without departing from the scope of the present disclosure.
Claims
1. A rotor configured to rotate about a longitudinal axis, the rotor comprising:
- a shaft disposed along the longitudinal axis; and
- a first re-entrant end attaching the shaft to a rotor torque tube; wherein at most a threshold fraction of a bending load applied to the shaft is communicated to a rotor active section comprising the rotor torque tube.
2. The rotor of claim 1, wherein the re-entrant end comprises a plurality of segments, wherein at least two of the segments are substantially parallel to each other.
3. The rotor of claim 1, further comprising:
- a drive end region;
- a non-drive end region; and
- a second re-entrant end attaching the shaft to the rotor torque tube; wherein the first re-entrant end is disposed proximate to the drive end region, and the second re-entrant end is disposed proximate to the non-drive end region.
4. The rotor of claim 3, wherein the first re-entrant end is disposed adjacent to a rotor cryostat, and the second re-entrant end is disposed adjacent to the rotor cryostat.
5. The rotor of claim 1, further comprising a winding configured to superconduct when at or below a superconducting temperature, wherein the rotor torque tube is disposed between the winding and the shaft, and wherein the re-entrant drive end increases a resistance to heat transfer between the shaft and the winding.
6. The rotor of claim 1, wherein a first point of the re-entrant drive end is at a room temperature, and a second point of the re-entrant drive end is at a superconducting temperature.
7. A superconducting electrical machine, comprising:
- a stator disposed coannular with a longitudinal axis, the stator defining a cavity;
- a rotor configured to rotate about the longitudinal axis and disposed at least partially within the cavity, the rotor comprising:
- a shaft configured to rotate with the rotor;
- a rotor active section comprising at least a rotor torque tube and a superconductor; and
- a first re-entrant end attaching the shaft to the rotor active section;
- wherein at most a threshold fraction of a bending load applied to the shaft is communicated to the rotor active section.
8. The superconducting electrical machine of claim 7, wherein the re-entrant end comprises a plurality of segments, wherein at least two of the plurality of segments are substantially parallel to each other.
9. The superconducting electrical machine of claim 7, further comprising:
- a drive end region;
- a non-drive end region; and
- a second re-entrant end attaching the shaft to the rotor torque tube, wherein the first re-entrant end is disposed proximate to the drive end region, and the second re-entrant end is disposed proximate to the non-drive end region.
10. The superconducting electrical machine of claim 9, wherein the first re-entrant end is disposed adjacent to a rotor cryostat, and the second re-entrant end is disposed adjacent to the rotor cryostat.
11. The superconducting electrical machine of claim 9, further comprising a pair of bearings disposed at the drive end region and the non-drive end region, the pair of bearings being configured to support the shaft and accommodate rotation of the shaft.
12. The superconducting electrical machine of claim 7, further comprising a winding configured to superconduct when at or below a superconducting temperature, wherein the rotor torque tube is disposed between the winding and the shaft, and wherein the re-entrant drive end increases a resistance to heat transfer between the shaft and the winding.
13. A system for generating electricity, comprising:
- a prime mover configured to rotate a shaft about a longitudinal axis; and
- a superconducting electrical machine, comprising: a stator disposed coannular with the longitudinal axis; and a rotor configured to rotate about the longitudinal axis, the rotor comprising the shaft, a rotor torque tube, and a rotor active section disposed surrounding and coannular with a rotor torque tube, wherein a first re-entrant end attaches the shaft to the rotor active section;
- wherein at most a threshold fraction of a bending load applied to the shaft by the prime mover is communicated to the rotor active section.
14. The system of claim 13, wherein the prime mover is a wind turbine.
15. The system of claim 13, wherein the shaft is configured to rotate at a rate greater than zero revolutions per minute and less than 100 revolutions per minute.
16. The system of claim 13, wherein the re-entrant end comprises a plurality of segments, wherein at least two of the plurality of segments are substantially parallel to each other.
17. The system of claim 13, wherein the rotor further comprises:
- a drive end region;
- a non-drive end region; and
- a second re-entrant attaching the shaft to the rotor torque tube, wherein the first re-entrant end is disposed proximate to the drive end region, and the second re-entrant end is disposed proximate to the non-drive end region.
18. The system of claim 17, wherein the first re-entrant end is disposed adjacent to a rotor cryostat, and the second re-entrant end is disposed adjacent to the rotor cryostat.
19. The system of claim 17, further comprising a pair of bearings disposed at the drive end region and the non-drive end region, the pair of bearings being configured to support the shaft and accommodate rotation of the shaft.
20. The system of claim 13, wherein the re-entrant end is configured to compensate for a volume change of the rotor due to a change in temperature from a first temperature to a second temperature.
Type: Application
Filed: Mar 18, 2015
Publication Date: Sep 22, 2016
Patent Grant number: 10270311
Inventor: Darrell Morrison (Eagle Lake, MN)
Application Number: 14/662,084